Increasingly, businesses and other entities are using virtualized computing resources (whether running on purchased or leased computer hardware). Virtualized environments are generally very dynamic—virtual machines can easily be spun up, shut down, and moved. As one example, instead of maintaining a set of dedicated physical machines to serve web pages, a business may run at least some virtualized webservers. In such a scenario, if additional demand is experienced, additional virtualized webservers can quickly be brought online to handle the increased traffic. Unfortunately, virtualized environments can pose problems for firewall rules which tend to rely on static information, such as static IP addresses.